Appliance with turbidity sensor assisted time interval determination

ABSTRACT

The present subject matter provides an appliance with features for determining a time interval for liquid flowing into and/or out of the appliance. For example, a flow of liquid into and/or out of a wash chamber of the appliance is initiated, and a first time is noted. A turbidity sensor is monitored until the sensor detects liquid or air respectively, and a second time is logged. A time interval is calculated based at least in part on the first time and the second time.

FIELD OF THE INVENTION

The present subject matter relates generally to appliances and relatedmethods that use a turbidity sensor to determine a time interval forliquid entering and/or exiting the appliances.

BACKGROUND OF THE INVENTION

With continued pressure on natural resources, appliance manufacturershave focused on efficiency in implementing new designs. Accordingly,appliance manufacturers have scrutinized the amount of electricity, theamount of detergent, and the amount of water used by their appliancesbecause these are all important factors in providing efficient andenvironmentally sensitive machines. In particular, one approach forimproving efficiency involves controlling and/or monitoring the amountof water used in various cycles of the appliances.

In order to accurately determine the amount of liquid (e.g., water) usedduring various cycles, a dishwasher appliance can rely on apredetermined estimate of the rate at which liquid enters and/or exitsthe appliance—i.e., the appliance's fluid fill rate and fluid drainrate. The dishwasher appliance can utilize such predetermined fluid filland drain rates to estimate the amount of liquid in the appliance. Forexample, the dishwasher may permit liquid to flow into the appliance fora predetermined amount of time in order to fill the appliance with aparticular volume of liquid (the time being chosen based upon thepredetermined fluid fill and drain rates).

However, variations in consumers' water valves, drain pumps, plumbedinlet flow rate, plumbed inlet pressure, and/or certain geometricconstraints can cause significant variation in the actual fill and drainrates between appliances. Thus, the actual fill and drain rates can besignificantly different (e.g., greater or less) than the predeterminedestimate of the appliance's fill and drain rates. Because the actualfill and drain rates can vary between appliances, the predeterminedestimate of the appliance's fill and drain rates are generally veryconservative and are often chosen such that the appliance overfills withliquid in order to ensure an adequate amount of liquid is provided tothe appliance during operation. Such overfill can result in excessiveand unnecessary water usage.

Previously, to avoid relying on predetermined estimated fill and drainrates, a flow meter has been used to measure the actual amount of liquidentering and/or exiting the appliance and, in turn, calculate actualfill and drain rates. However, such flow meters can add to the overallcost of producing the appliance. Also, flow meters can requirecalibration in order to accurately measure the amount of water enteringand/or exiting the appliance. Calibrations can be time consuming andinconvenient. Further, flow meters can malfunction and require repair inorder to function properly.

Accordingly, an appliance that determines the amount of liquid in theappliance would be useful. Also, an appliance that determines the amountof liquid in the appliance without relying on predetermined estimatedfill and drain rates would be useful. In addition, an appliance thatdetermines the amount of liquid in the appliance without relying on aflow meter would be useful. An appliance that can determine the amountof liquid in the appliance without requiring additional measuringdevices would be particularly useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In a first embodiment, a dishwasher appliance is provided with a cabinetthat defines a wash chamber. The cabinet includes a sump positionedadjacent a bottom of the cabinet. The sump is configured for collectingliquid in the wash chamber. A rack assembly is slidably received intothe wash chamber and configured for receipt of articles for cleaning. Aspray arm assembly is also provided for applying the liquid to thearticles in the rack assembly. An inlet is also provided that isconfigured for selectively adding liquid to the wash chamber of thecabinet. A turbidity sensor is disposed within the sump of the cabinetand configured for measuring a turbidity of fluid in the sump. Aprocessing device is in communication with the inlet and the turbiditysensor. The processing device is configured for adjusting the inlet inorder to initiate the flow of liquid into the wash chamber of thecabinet, noting a first time, t₁, that corresponds to the step ofadjusting, detecting liquid with the turbidity sensor, logging a secondtime, t₂, that corresponds to the step of detecting, and determining atime interval based at least in part on t₁ and t₂.

In a second embodiment, a method for operating an appliance is provided.The method includes initiating a flow of a liquid into a sump of theappliance, noting a first time, t₁, that corresponds to about the stepof initiating, detecting the liquid with a turbidity sensor, logging asecond time, t₂, that corresponds to about the step of detecting, anddetermining a time interval based at least in part upon t₁ and t₂.

In a third embodiment, a method for operating an appliance is provided.The method includes initiating a flow of a liquid out of a sump of theappliance, noting a first time, t₁, that corresponds to about the stepof initiating, detecting air with a turbidity sensor, logging a secondtime, t₂, that corresponds to about the step of detecting, anddetermining a time interval based at least in part upon t₁ and t₂.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 provides a perspective view of a dishwasher appliance accordingto an exemplary embodiment of the present subject matter.

FIG. 2 is a side cross-sectional view of the exemplary dishwasherappliance of FIG. 1.

FIG. 3 provides a cross-sectional view of a sump of the exemplarydishwasher appliance of FIG. 2.

FIG. 4 illustrates an exemplary method for operating a dishwasherappliance according to an embodiment of the present subject matter.

FIG. 5 illustrates an additional exemplary method for operating adishwasher appliance according to an embodiment of the present subjectmatter.

DETAILED DESCRIPTION OF THE INVENTION

The present subject matter provides an appliance with features fordetermining a time interval for liquid flowing into and/or out of theappliance. For example, a flow of liquid into and/or out of a washchamber of the appliance is initiated, and a first time is noted. Aturbidity sensor is monitored until the sensor detects liquid or airrespectively, and a second time is logged. A time interval is calculatedbased at least in part on the first time and the second time. Referencenow will be made in detail to embodiments of the invention, one or moreexamples of which are illustrated in the drawings. Each example isprovided by way of explanation of the invention, not limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations can be made in the presentinvention without departing from the scope or spirit of the invention.For instance, features illustrated or described as part of oneembodiment can be used with another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

FIGS. 1 and 2 depict an exemplary domestic dishwasher appliance 100 thatmay be configured in accordance with aspects of the present disclosure.For the particular embodiment of FIG. 1, the dishwasher 100 includes acabinet 102 that extends between a front 114 and a back 116. The cabinet102 also extends between a top 110 and a bottom 112. The cabinet 102 hasa tub 104 therein that defines a wash chamber 106. The tub 104 includesa front opening (not shown) and a door 120 hinged at its bottom 122 formovement between a normally closed, vertical position (shown in FIGS. 1and 2), wherein the wash chamber 106 is sealed shut for washingoperation, and a horizontal, open position for loading and unloading ofarticles from the dishwasher. Latch 123 is used to lock and unlock door120 for access to chamber 106. Tub 104 also includes (e.g., defines) asump 200 positioned adjacent bottom 112 of cabinet 102 and configuredfor receipt of a liquid (e.g., water, detergent, washing fluid, and/orany other suitable fluid) during operation of appliance 100.

An inlet 160 is positioned adjacent sump 200 of appliance 100. Inlet 160is configured for directing liquid into sump 200. Inlet 160 may receiveliquid from, e.g., a water supply (not shown) or any other suitablesource. In alternative embodiments, inlet 160 may be positioned at anysuitable location within appliance 100 such that inlet 160 directsliquid into tub 104. Inlet 160 may include a valve (not shown) such thatliquid may be selectively directed into tub 104. Thus, for example,during the cycles described below, inlet 160 may selectively directwater and/or washing fluid into sump 200 as required by the currentcycle of the appliance 100.

Rack assemblies 130 and 132 are slidably mounted within the wash chamber106. Each of the rack assemblies 130, 132 is fabricated into latticestructures including a plurality of elongated members 134. Each rack130, 132 is adapted for movement between an extended loading position(not shown) in which the rack is substantially positioned outside thewash chamber 106, and a retracted position (shown in FIGS. 1 and 2) inwhich the rack is located inside the wash chamber 106. A silverwarebasket (not shown) may be removably attached to rack assembly 132 forplacement of silverware, utensils, and the like, that are otherwise toosmall to be accommodated by the racks 130, 132.

The dishwasher 100 further includes a lower spray-arm assembly 144 thatis rotatably mounted within a lower region 146 of the wash chamber 106and above a tub sump portion 142 so as to rotate in relatively closeproximity to rack assembly 132. A mid-level spray-arm assembly 148 islocated in an upper region of the wash chamber 106 and may be located inclose proximity to upper rack 130. Additionally, an upper spray assembly150 may be located above the upper rack 130.

The lower and mid-level spray-arm assemblies 144, 148 and the upperspray assembly 150 are fed by a fluid circulation assembly 152 forcirculating water and dishwasher fluid in the tub 104. The fluidcirculation assembly 152 may include a drain pump 220 located in amachinery compartment 140 located below the bottom sump portion 142 ofthe tub 104, as generally recognized in the art. Each spray-arm assembly144, 148 includes an arrangement of discharge ports or orifices fordirecting washing liquid onto dishes or other articles located in rackassemblies 130 and 132. The arrangement of the discharge ports inspray-arm assemblies 144, 148 provides a rotational force by virtue ofwashing fluid flowing through the discharge ports. The resultantrotation of the lower spray-arm assembly 144 provides coverage of dishesand other dishwasher contents with a washing spray.

The dishwasher 100 is further equipped with a controller 137 to regulateoperation of the dishwasher 100. The controller may include a memory andmicroprocessor, such as a general or special purpose microprocessoroperable to execute programming instructions or micro-control codeassociated with a cleaning cycle. The memory may represent random accessmemory such as DRAM, or read only memory such as ROM or FLASH. In oneembodiment, the processor executes programming instructions stored inmemory. The memory may be a separate component from the processor or maybe included onboard within the processor.

The controller 137 may be positioned in a variety of locationsthroughout dishwasher 100. In the illustrated embodiment, the controller137 may be located within a control panel area 121 of door 120 as shown.In such an embodiment, input/output (“I/O”) signals may be routedbetween the control system and various operational components ofdishwasher 100 along wiring harnesses that may be routed through thebottom 122 of door 120. Typically, the controller 137 includes a userinterface panel 136 through which a user may select various operationalfeatures and modes and monitor progress of the dishwasher 100. In oneembodiment, the user interface 136 may represent a general purpose I/O(“GPIO”) device or functional block. In one embodiment, the userinterface 136 may include input components, such as one or more of avariety of electrical, mechanical or electro-mechanical input devicesincluding rotary dials, push buttons, and touch pads. The user interface136 may include a display component, such as a digital or analog displaydevice designed to provide operational feedback to a user. The userinterface 136 may be in communication with the controller 137 via one ormore signal lines or shared communication busses.

It should be appreciated that the subject matter disclosed herein is notlimited to any particular style, model, or other configuration ofdishwasher, and that the embodiment depicted in FIGS. 1 and 2 is forillustrative purposes only. For example, instead of the racks 130, 132depicted in FIG. 1, the dishwasher 100 may be of a known configurationthat utilizes drawers that pull out from the cabinet and are accessiblefrom the top for loading and unloading of articles. In addition, itshould be understood that the subject matter disclosed herein is notlimited to dishwasher appliances and may be utilized in, e.g., washingmachine appliances.

FIG. 3 provides a cross-sectional view of sump 200 of dishwasherappliance 100. Sump 200 extends between a top 206 and a bottom 208. Sump200 includes a reservoir 230 configured for receipt of liquid duringoperation of appliance 100. Drain pump 220 is positioned adjacent bottom208 of sump 200 and is in fluid communication with reservoir 230 of sump200. Thus, liquid disposed in sump 200 may be selectively removed (i.e.,drained) from sump 200 by drain pump 220.

Sump 200 also includes a turbidity sensor 210. Turbidity sensor 210 isconfigured for measuring turbidity of a fluid in reservoir 230 of sump200. For example, turbidity sensor 210 may output a signal (e.g., avoltage or current) to controller 137 corresponding to a turbidity ofliquid measured by turbidity sensor 210. Turbidity sensor 210 can alsobe used to provide an output signal indicative of when sump 200 isempty. More specifically, turbidity sensor 210 can be used to determinewhen sensor 210 is measuring air as oppose to a liquid. Similarly,turbidity sensor 210 can be used to determine when sensor 210 ismeasuring both air and a liquid.

A drain level 204 is shown in FIG. 3. Drain level 204 corresponds to alevel of liquid that remains in reservoir 230 of sump 200 afteractivation of drain pump 220. For example, drain pump 220 may not becapable of removing all liquid from reservoir 230 of sump 200. Thus, avolume of liquid that fills sump 200 to drain level 204 represents acarryover volume, V_(c) that can remain in sump 200 despite activationof drain pump 220 to remove liquid from reservoir 230. V_(c) may bemeasured in order to accurately determine the amount of liquid remainingin sump 200 after activation of drain pump 220. For example, duringdesign or manufacture of sump 200, V_(c) may be measured or calculated.

A fill level 202 is also shown in FIG. 3. Fill level 202 corresponds toa level of liquid used in any particular cycle of appliance 100. As willbe understood by those skilled in the art, fill level 202 may vary. Forexample, the specific fill level 202 for any particular cycle may dependon the current cycle (e.g., wash or rinse) of the appliance 100, therelative dirtiness of articles being washed by appliance 100, and/or theamount of articles being washed by appliance 100. Thus, fill level 202may be higher than as shown, even extending above sump 200, and isrepresented in FIG. 3 by way of example only. Accordingly, a volume ofliquid that fills sump 200 to fill level 202 represents a prime volume,V_(p), of liquid disposed in the appliance 100 during a given cycle ofoperation of appliance 100. V_(p) may be measured in order to accuratelydetermine the amount of liquid in sump 200 during operation of appliance100. For example, during design or manufacture of sump 200, V_(p) may bemeasured or calculated. Alternatively, V_(p) may be calculated basedupon a fluid flow rate as described in greater detail below.

As described above, the output of turbidity sensor 210 changes withcorresponding changes in the turbidity of fluid being measured byturbidity sensor 210 and with changes between measuring a liquid versusmeasuring air or a liquid and air. Accordingly, turbidity sensor 210 hasa different output depending upon whether it is measuring liquid, air,or a combination of liquid and air. For example, when turbidity sensor210 is exposed to washing fluid (e.g., water and/or detergent), theoutput of turbidity sensor 210 is significantly different compared tothe output of turbidity sensor 210 when exposed to air or liquid and airas can occur as the liquid level changes.

As may be seen in FIG. 3, turbidity sensor 210 has a detection range212. Turbidity sensor 210 can only measure turbidity of fluid disposedwithin the detection range 212. Detection range 212 includes a maximumdetection height 214 and a minimum detection height 216. The minimumdetection height 216 corresponds to a height below which the turbiditysensor 210 cannot measure the turbidity of fluid. For example, duringfilling of reservoir 230 with liquid from inlet 160, output of turbiditysensor 210 will change when the liquid reaches the minimum detectionheight 216 because when liquid passes the minimum detection height 216,turbidity sensor 210 begins to measure the turbidity of the liquidinstead of only air.

Accordingly, a volume of liquid that fills the sump 200 to minimumdetection height 216 corresponds to a turbidity sensor fill volume,V_(tsf), of liquid—i.e. the amount of liquid that must be placed intoappliance 100 and/or sump 200 before turbidity sensor 210 detects achange between measuring only air versus measuring both air and liquid.V_(tsf) may be measured in order to accurately determine the amount ofliquid in sump 200 below minimum detection height 216. For example,during design or manufacture of sump 200, V_(tsf) may be measured orcalculated. In alternative embodiments, V_(tsf) may correspond to anysuitable volume that turbidity sensor 210 may reliably detect duringfilling of sump 200 with liquid, e.g., a volume of liquid that fillsreservoir 230 to maximum detection height 214.

The maximum detection height 214 of turbidity sensor 210 corresponds toa height above which the turbidity sensor 210 cannot be used to detectchanges in the level of liquid in the appliance 100. However, duringdraining of sump 200, turbidity sensor 210 may determine when liquid insump 200 drops below maximum detection height 214. For example, duringdraining of reservoir 230 from fill level 202, output of turbiditysensor 210 will change when liquid (e.g., washing fluid) passes themaximum detection height 214 and the turbidity sensor 210 is exposed toair and liquid instead of just liquid.

Accordingly, a volume of liquid that fills sump 200 to maximum detectionheight 214 corresponds to a turbidity sensor drain volume, V_(tsd)—i.e.the volume of liquid that must remain in sump 200 for turbidity sensor210 to measure only liquid rather than only air or air and liquid.V_(tsd) may be measured in order to accurately determine the amount ofliquid in sump 200 at the maximum detection height 214. For example,during design or manufacture of sump 200, V_(tsd) may be measured orcalculated. In alternative embodiments, V_(tsd) may correspond to anysuitable volume that turbidity sensor 210 may reliably detect duringdraining of sump 200, e.g., a volume of liquid that fills reservoir 230to minimum detection height 214.

FIG. 4 illustrates an exemplary method 400 for operating a dishwasherappliance, e.g., appliance 100. In method 400, a time interval, Δt, isprovided. Δt can be used to estimate the amount of liquid (e.g., water)entering appliance 100. Knowledge of the amount of liquid in appliance100 can permit appliance 100 to operate more efficiently by utilizing anoptimum amount of liquid for any particular cycle of the appliance 100.For example, if dishwasher 100 has a small load of articles in washchamber 106, less water is needed to clean such a load compared to alarge load of articles. Thus, appliance 100 can use less water to cleansuch a load. Method 400 can provide an accurate estimate of the amountof liquid entering appliance 100. Also, method 400 utilizes turbiditysensor 210 to calculate Δt. By utilizing turbidity sensor 210 ratherthan another additional sensor (e.g., a flow meter), appliance 100 canbe more reliable and/or cheaper to produce.

Controller 137 may be programmed to complete or perform the steps ofmethod 400. At 410, a flow of liquid into sump 200 of appliance 100 isinitiated. For example, controller 137 may initiate the flow of liquidby adjusting inlet 160. However, initiating the flow of liquid into sump200 may be accomplished via any suitable method.

At 420, a first time, t₁, is recorded. For example, controller 137 mayrecord t₁ when inlet 160 is adjusted at 410 and liquid begins to flowinto sump 200. Thus, t₁ corresponds to about a time when liquid beginsflowing into sump 200.

At 430, output from turbidity sensor 210 is monitored. Based on outputof turbidity sensor 210, at 440, it is determined whether turbiditysensor 210 is still detecting only air or is also detecting a liquid. Asdiscussed above, the output of turbidity sensor 210 changes withcorresponding changes in the turbidity of fluid being measured byturbidity sensor 210 as well as changes from air to liquid or viceversa. Accordingly, turbidity sensor 210 will have a different outputwhen exposed to liquid from inlet 160 compared to just air. Thus,controller 137 may detect a change in turbidity sensor 210 output asliquid passes the minimum detection line 216 and infer that turbiditysensor 210 is now sensing liquid and air.

At 450, a second time, t₂, is recorded. For example, controller 137 mayrecord t₂ when turbidity sensor 210 detects liquid from inlet 160 instep 440. Thus, t₂ may correspond to about a time when liquid from inlet160 fills reservoir 230 of sump 200 to minimum detection height 216,which corresponds to fluid fill volume V_(tsf).

At 460, time interval, Δt, is calculated as

Δt _(□) =t ₂ −t ₁.  (1)

However, alternative formulas may also be used to calculate Δt. Δt iscalculated at 460 to provide a measured value for the amount time neededfor liquid entering sump 200 via inlet 160 to reach minimum detectionlevel 216. With accurate Δt, appliance 100 may permit a specific amountof liquid to enter into sump 200 through inlet 160.

At 470, Δt is compared to a stored value. Thus, controller 137 maycompare Δt to the stored value. At 480, if Δt is significantly differentfrom stored value, controller 137 may replace the stored value with Δt.The stored value may be used, e.g., to estimate the amount of liquidentering sump 200. However, the stored value may be replace with Δt thathas been calculated to more accurately reflect time needed for liquid toenter the sump 200 via inlet 160.

In additional embodiments, steps 410-450 may be repeated to generate aplurality of t₁ and a plurality of t₂. For example, steps 410-450 may berepeated two, three, four, five, or more times in order to generate arespective number of t₁ and t₂. At 460, the plurality of t₁ and theplurality of t₂ may be used to calculate Δt. By utilizing the pluralityof t₁ and the plurality of t₂ at 460, Δt may be averaged and thus bemore accurate.

In alternative embodiments, at 430, rather than detecting liquid frominlet 160 reaching minimum detection height 216, turbidity sensor 210 iscalibrated such that liquid filling sump 200 to maximum detection height214 results in a specific output (e.g., voltage or current) fromturbidity sensor 210. Controller 137 may receive such specific outputfrom turbidity sensor 210 and determine that liquid from inlet 160 hasfilled sump 200 to maximum detection height 214. For example, asdetection range 212 is submerged in liquid from inlet 160 and the liquidapproaches the maximum detection height 214, output from turbiditysensor 210 may approach the specific output, and controller 137 mayinfer that turbidity sensor 210 is detecting only liquid and, therefore,liquid has reached maximum detection height 214 and fills volumeV_(tsf).

In additional alternative embodiments, at 460, rather than Δt, a fluidfill rate, F_(fill), is calculated as

$\begin{matrix}{\text{?}{\text{?}\text{indicates text missing or illegible when filed}}} & (2)\end{matrix}$

where V_(tsf) is the turbidity sensor fill volume and V_(c) is thecarryover volume. Alternative formulas may also be used to calculateF_(fill). F_(fill) may be calculated at 460 to provide a measured valuefor rate at which liquid enters sump 200 via inlet 160. Thus, withaccurate F_(fill), appliance 100 may permit a specific amount of liquidinto sump 200 through inlet 160.

As discussed above, V_(P) may be calculated based upon a fluid flowrate. For example, with F_(fill) measured using the above method 400,F_(fill) may be used to calculate V_(p). For example, controller 137 mayadjust inlet 160 such that liquid is entering sump 200. As will beunderstood by those skilled in the art, with F_(fill) known, controller137 may permit liquid to enter sump 200 for a specific amount of timesuch that a particular V_(p) fills reservoir 230.

FIG. 5 illustrates another exemplary method 500 for operating adishwasher appliance, e.g., appliance 100. In method 500, an additionaltime interval, Δt_(a), is calculated. Δt_(a) can be used to estimate theamount of liquid (e.g., water or washing fluid) exiting appliance 100.Knowledge of the amount of liquid exiting appliance 100 can permitappliance 100 to operate more efficiently by utilizing an optimum amountof liquid for any particular cycle of the appliance 100. For example, ifdishwasher 100 has a small, relatively clean load of articles in washchamber 106, washing fluid used to clean such articles may be relativelyclean at an end of the wash cycle. Because the washing fluid isrelatively clean, the washing fluid can also be used to rinse thearticles by adding a small amount of clean water to the washing fluid.Method 500 can be used to estimate the amount of washing fluid exitingappliance 100 prior to adding the clean water for rinsing. Also, method500 also utilizes turbidity sensor 210 to calculate Δt_(a). By utilizingturbidity sensor 210 rather than another additional sensor (e.g., a flowmeter), appliance 100 can be more reliable and/or cheaper to produce.

Controller 137 may be programmed to complete or perform the steps ofmethod 500. At 510, a flow of liquid out of sump 200 of appliance 100 isinitiated. For example, controller 137 may activate drain pump 220 inorder to begin draining reservoir 230 of liquid when liquid fillsreservoir 230 to fill level 202. However, initiating the flow of liquidout of sump 200 may also be accomplished via any other suitable method.

At 520, an additional first time, t_(1a), is recorded. For example,controller 137 may record t_(1a) when drain pump 220 is activated at 510and liquid begins to flow out of sump 200. Thus, t_(1a) corresponds toabout a time when liquid begins flowing out of sump 200.

At 530, an output from turbidity sensor 210 is monitored. Based onoutput of turbidity sensor 210, at 540, it is determined whetherturbidity sensor 210 is detecting liquid. For example, controller 137may determine whether turbidity sensor 210 is still sensing only liquiddisposed in sump 200 or whether drain pump 220 has removed sufficientliquid from reservoir 230 such that at least part of detection range 212of turbidity sensor 210 is exposed to air.

As discussed above, the output of turbidity sensor 210 changes withcorresponding changes in the turbidity of fluid being measured byturbidity sensor 210 as well as changes from air to liquid or viceversa. Accordingly, turbidity sensor 210 will have a different outputwhen exposed to liquid compared to just air. Thus, controller 137 maydetect a change in turbidity sensor 210 output as liquid drains passedthe maximum detection height 214 and at least a portion of detectionrange 212 of turbidity sensor 210 is exposed to air to infer thatturbidity sensor 210 is now sensing air and liquid rather than onlyliquid.

At 550, an additional second time, t_(2a), is recorded. For example,controller 137 may record t_(2a) when turbidity sensor 210 detects airat 540. Thus, t_(2a) may correspond to about a time when drain pump 220has removed liquid from sump 200 such that the level of liquid in thesump 200 passes the maximum detection height 214, which corresponds tofluid drain volume V_(tsd).

At 560, an additional time interval, Δt_(a), is calculated as

Δt _(a□) =t _(2a) −t _(1a).  (3)

However, alternative formulas may also be used to calculate Δt_(a).Δt_(a) is calculated at step 560 to provide a measured value for theamount of time necessary for liquid to exit sump 200 via drain pump 220.With accurate Δt_(a), appliance 100 may drain a specific amount ofliquid from sump 200.

At 570, Δt_(a) is compared to a stored value. Thus, controller 137 maycompare Δt_(a) to the stored value. At 580, if Δt_(a) is significantlydifferent from stored value, controller 137 may replace the stored valuewith Δt_(a). The stored value may be used, e.g., to estimate the amountof liquid exiting sump 200. However, the stored value may be replacedwith Δt_(a) that has been calculated to more accurately reflect timeneeded for liquid to exit sump 200 via drain pump 220.

In additional embodiments, steps 510-550 may be repeated to generate aplurality of t_(1a) and a plurality of t_(2a). For example, steps510-550 may be repeated two, three, four, five, or more times in orderto generate a respective number of t_(1a) and t_(2a). At 560, theplurality of t_(1a) and the plurality of t_(2a) may be used to calculateΔt_(a). By utilizing the plurality of t_(1a) and the plurality of t_(2a)at 560, Δt_(a) may be averaged and thus be more accurate.

In alternative embodiments, at 530, rather than detecting liquiddraining from sump 200 passing maximum detection height 214, turbiditysensor 210 is calibrated such that turbidity sensor 210 sensing only airthroughout detection range 212 results in a specific output (e.g.,voltage or current) from turbidity sensor 210. Controller 137 mayreceive such specific output from turbidity sensor 210 and determinethat drain pump has drained sump 200 of liquid such that liquid hasdrained passed the minimum detection height 216. For example, asdetection range 212 drains of liquid, output from turbidity sensor 210may approach the specific output, and controller 137 may infer thatturbidity sensor 210 is exposed to only air, and, therefore liquid hasdrained passed the minimum detection height 216.

In additional alternative embodiments, at 560, rather than Δt_(a), afluid drain rate, F_(drain), is calculated as

$\begin{matrix}{F_{drain} - \frac{V_{p} - V_{tsf}}{t_{2c} - t_{1c}}} & (4)\end{matrix}$

where V_(tsd) is the turbidity sensor drain volume and V_(p) is theprime volume. Alternative formulas may also be used to calculateF_(drain). F_(drain) may be calculated at step 560 to provide a measuredvalue for the rate at which drain pump 220 removes liquid from sump 200.With accurate F_(drain), appliance 100 may drain a specific amount ofliquid from sump 200.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A dishwasher appliance comprising: a cabinetdefining a wash chamber, said cabinet including a sump positionedadjacent a bottom of said cabinet, the sump configured for collectingliquid in the wash chamber; a rack assembly slidably received into thewash chamber and configured for receipt of articles for cleaning; aspray arm assembly for applying the liquid to the articles in said rackassembly; an inlet configured for selectively adding liquid to the washchamber of said cabinet; a turbidity sensor disposed within the sump ofsaid cabinet and configured for measuring a turbidity of fluid in thesump; and a processing device in communication with said inlet and saidturbidity sensor, wherein said processing device is configured for:adjusting said inlet in order to initiate the flow of liquid into thewash chamber of said cabinet; noting a first time, t₁, that correspondsto said step of adjusting; detecting liquid with said turbidity sensor;logging a second time, t₂, that corresponds to said step of detecting;and determining a time interval based at least in part on t₁ and t₂. 2.The dishwasher appliance of claim 1, wherein said processing device isfurther configured for calculating a fluid flow rate based at least inpart on t₁ and t₂.
 3. The dishwasher appliance of claim 2, wherein saidprocessing device is further configured for comparing the fluid flowrate to a stored fluid flow rate.
 4. The dishwasher appliance of claim3, wherein said processing device is further configured for replacingthe stored fluid flow rate with the fluid flow rate if the stored fluidflow rate is significantly different from the fluid flow rate.
 5. Thedishwasher appliance of claim 1, wherein said processing device isfurther configured for repeating said steps of adjusting, noting,detecting, and logging in order to generate a plurality of t₁ and aplurality of t₂, said processing device determining the time intervalbased at least in part on the plurality t₁ and the plurality of t₂. 6.The dishwasher appliance of claim 1, further comprising a drainconfigured for draining the sump of said cabinet of liquid, wherein saidprocessing device is further configured for: opening said drain in orderto initiate a flow of the liquid out of the sump of said cabinet;recording an additional first time, t_(1a), that corresponds to aboutsaid step of opening; sensing air with said turbidity sensor;chronicling an additional second time, t_(2a), that corresponds to aboutsaid step of sensing; establishing an additional time interval based atleast in part on t_(1a) and t_(2a).
 7. The dishwasher appliance of claim6, wherein said processing device is further configured for computing anadditional fluid flow rate based at least in part on t_(1a) and t_(2a).8. The dishwasher appliance of claim 7, wherein said processing deviceis further configured for comparing the additional fluid flow rate to anadditional stored fluid flow rate.
 9. The dishwasher appliance of claim6, wherein said processing device is further configured for repeatingsaid steps of opening, recording, sensing, and chronicling in order togenerate a plurality of t_(1a) and a plurality of t_(2a), saidprocessing device determining the additional fluid flow rate based atleast in part on the plurality of t_(1a) and plurality of t_(2a).
 10. Amethod for operating an appliance, the method comprising: initiating aflow of a liquid into a sump of the appliance; noting a first time, t₁,that corresponds to about said step of initiating; detecting the liquidwith a turbidity sensor; logging a second time, t₂, that corresponds toabout said step of detecting; and determining a time interval based atleast in part upon t₁ and t₂.
 11. The method of claim 10, furthercomprising calculating a fluid flow rate of the liquid based at least inpart upon t₁ and t₂.
 12. The method of claim 11, further comprisingcomparing the fluid flow rate to a prior fluid flow rate.
 13. The methodof claim 11, further comprising replacing the prior fluid flow rate withthe fluid flow rate if the prior fluid flow rate is significantlydifferent from the fluid flow rate.
 14. The method of claim 10, furthercomprising: repeating said steps of adjusting, noting, detecting, andlogging in order to generate a plurality of t₁ and a plurality of t₂;and determining the time interval based at least in part on theplurality of t₁ and the plurality of t₂.
 15. A method for operating anappliance, the method comprising: initiating a flow of a liquid out of asump of the appliance; noting a first time, t₁, that corresponds toabout said step of initiating; detecting air with a turbidity sensor;logging a second time, t₂, that corresponds to about said step ofdetecting; and determining a time interval based at least in part upont₁ and t₂.
 16. The method of claim 15, further comprising calculating afluid flow rate of the liquid based at least in part upon t₁ and t₂. 17.The method of claim 16, further comprising comparing the fluid flow rateto a prior fluid flow rate.
 18. The method of claim 16, furthercomprising replacing the prior fluid flow rate with the fluid flow rateif the prior fluid flow rate is significantly different from the fluidflow rate.
 19. The method of claim 15, further comprising: repeatingsaid steps of initiating, noting, detecting, and logging in order togenerate a plurality of t₁ and a plurality of t₂; and determining thetime interval based at least in part on the plurality of t₁ and theplurality of t₂.